In order to reduce future environmental loads on automobiles, a combustion control technique for making it possible to highly control generation of a toxic substance in in-cylinder combustion of an engine is needed. Therefore, it is necessary to accurately grasp an amount of suction air into the engine, and higher precision is being desired in a fluid measurement device that is represented by a flow sensor.
As the fluid measurement device for automobile, a thermal type flow sensor is known. The thermal type flow sensor is a device in which a heating element is arranged in a fluid and a flow rate is measured by detecting a change in temperature around the heating element caused by a flow. It is known that the output characteristic of this thermal type flow sensor fluctuates in accordance with the temperature, the pressure and so forth of the fluid, and correction techniques according to the temperature, the pressure and so forth have been proposed so far. There is a technique disclosed, for example, by Patent Literature 1.
The thermal type flow sensor described in Patent Literature 1 has a temperature detection unit that obtains a temperature t of a fluid that flows through a passage in order to correct a detected parameter v, and correction means that is provided with a correction table that has stored a correction value ΔX (v, t) per unit temperature relevant to the detected parameter v and the fluid temperature t and corrects the parameter v to a flow rate at a reference temperature tθ by setting a flow rate V after corrected asV=v+ΔX(v,t)·(t−tθ)
in accordance with v and t and ΔX (v, t).
In addition, the same also applies to pressure correction, and it has a pressure detection unit that obtains a pressure p of the fluid that flows through the passage in order to correct the detected parameter v, and correction means that is provided with a correction table that has stored a correction value ΔY (v, p) per unit temperature relevant to the detected parameter v and the fluid pressure p and corrects the parameter v to a flow rate at a reference pressure pθ by setting the flow rate V after corrected asV=v+ΔY(v,p)·(p−pθ)
in accordance with v and p and ΔY (v, p).